1) Field of the Invention
This invention relates to rock boring machines and, in particular, to a new cutter head construction for such a machine.
2) Description of the Prior Art
One of the challenges facing the mining industry today is the development of a mechanical miner for hard rock mining that is both effective and mobile. This challenge arises from the increasing costs of labor, supplies, and environmental effects. Current hard rock mining methods are expensive and slow.
Current mechanical miners can be classified into two groups: continuous miners and boring machines. Continuous miners employ a drum-type cutter with drag bits. Although continuous miners are mobile and effective in soft rock such as coal, they cannot cut hard rock such as limestone and quartzite. Some examples of these types of miners are disclosed in U.S. Pat. Nos. 2,792,204 and 2,808,253. Boring machines use a rotary cutter with disc cutters or button bits. Boring machines are effective in hard rock, but are very immobile. Two examples of boring machines are Tunnel Boring Machines (TBM) and raise borers (see U.S. Pat. Nos. 3,139,148; 4,192,556; 4,193,637; and 4,784,438).
The most important factor in mechanical mining is the compressive strength of the rocks. The higher the compressive strength of the rock, the harder it is to mine. The basic cutting action of mechanical miners is for the bit to penetrate the rock by using compressive forces to break it down, and then shearing off pieces of rock as the cutter head rotates. Therefore, the success or failure of a mechanical miner hinges on whether or not it can overcome the compressive strength of the rock. This is the reason why present hard rock borers are very large and immobile. Their size enables them to put forth a very large thrust force which is needed to overcome rocks with compressive strengths from 15,000 psi to 40,000 psi. The immobility of these boring machines renders these machines ineffective and impractical in conventional, labor intensive drill and blast methods.
Since rocks are significantly weaker in tension than they are in compression, an important factor for successful hard rock mechanical mining is to break rocks using tensile forces, not compressive forces. For example, even when blasting, rocks must be subjected to tensile forces. This is accomplished by strategically placing bore holes on a rock face which are not loaded with explosives and by delaying the detonation of the placed explosives. Hence, the cost to mine hard rock is extremely costly and dangerous.
Therefore, it is an object of my invention to provide a hard rock mining apparatus to overcome the conventional, labor intensive, drill and blast methods.
It is a further object of my invention to provide a hard rock mining apparatus which safely and economically mines hard rock.